AR15 rifles are currently one of the most popular rifles in the US. The fully automatic M16 version of this rifle was developed for, and adopted by the US military in 1963 and has been our primary battle rifle since. Because of the M16's military success and long service, a substantial industry has grown to produce and customize this weapon platform in numerous ways. In addition to its longevity, the rifle's modularity further lends itself to customization, since aftermarket parts & accessories easily bolt on.
Prior to 1967, the US used a heavier, 11.5 lb., M14 rifle that used the much more powerful 7.62 NATO cartridge; now the typical M16 weighs 7.8 lbs. In searching for a new weapons platform, the army sought a smaller, lighter rifle that recoiled less and used lighter ammunition, allowing troops to carry more ammo and gear. Thus, the M16 was downsized to use the smaller 5.56 mm NATO round, satisfying the army's desire for a more petite, lighter recoiling rifle that used lighter ammunition.
The AR15 platform is simple to accessorize and change calibers. The small 5.56 mm cartridge has served the US military well, but civilians and government agencies, have sought to fit larger cartridges into the AR15/M16. These large cartridges produce uncomfortable recoil that makes the small, light rifle painful to shoot. The most popular large calibers are the 0.50 Beowulf, 0.450 Bushmaster, and 0.458 SOCO M. The larger calibers have significant recoil; and as a result, transfer that energy to the shooter's shoulder. The US Coast Guard has adopted one of the larger calibers to enable them to disable boats by shooting and breaking their engine blocks with the AR15.
The larger and heavier rounds produce significantly more recoil energy than the standard round, up to ten times more. Although others have placed shock absorption systems within the small area available in the rifle stock, the current systems do not adequately absorb recoil energy due in part to insufficient compression. What is needed is recoil system that can absorb large amounts of recoil energy through a large compression, while maintaining the compact design requirements of the M16/AR15 rifles or similar long guns.
Standard AR15 collapsible stocks are designed to telescope (slide forward and back) on the buffer tube to adjust the length of pull of the rifle. The length of pull of the rifle is the length from the trigger to the end of the stock which rests against the shooter's shoulder. The length of pull is adjusted to accommodate large to small-framed people, and to adjust to the thickness of clothing layers or body armor donned. The standard stock may be incrementally adjusted and locked in place with a standard spring-biased detent pin that engages one of the detent holes in a line of detent holes to prevent forward and back movement of the stock. To adjust the stock, the detent pin may be disengaged from a detent hole through actuation of the connected latch.
The buffer tube is a required part of the AR15/A16 rifle. Since the buffer tube houses the buffer spring and the buffer, there is insufficient space within the buffer tube to install a shock absorption means. Manufacturers have tried to place a shock absorption system internally within the stock, behind the buffer tube. However, due to the limited space and short length behind the buffer tube, the shocks installed have insufficient stroke length over which larger caliber round recoil may be absorbed. Once the current shocks are at full compression during large recoil, the unabsorbed energy is then transferred to the shooter. Basically, the shock absorbers are limited in compression due to the limited space near and behind the buffer tube, making the large caliber rounds uncomfortable to fire.